Functional MRI determination of a dose-response relationship to lower extremity neuromuscular electrical stimulation in healthy subjects. (2003)

Abstract
Although empirical evidence supports the use of neuromuscular electrical stimulation (NMES) to treat physical impairments associated with stroke, the mechanisms underlying the efficacy of this modality are poorly understood. Recent studies have employed functional imaging to investigations of brain responses to median nerve stimulation. These studies suggest a dose-response relationship may exist between selected stimulation parameters and hemodynamic responses in sensorimotor regions. However, substantial gaps exist in this literature. The present study was designed to address these deficiencies. Ten healthy subjects participated. In phase one, four stimulus intensity levels were established: (1). sensory threshold [Th], (2). (MM-Th)x0.333+Th [low-intermediate level, LI], (3). (MM-Th)x0.666+Th [high-intermediate level, HI], and (4). maximal motor (MM). In phase two, subjects were scanned using a spiral-echoplanar imaging technique at each stimulus level. Image sets were analyzed to determine hemodynamic responses at the highest Pearson correlation level ( r) ascertained for each of five areas of interest (AOI): (1). primary sensory, (2). primary motor, (3). cingulate gyrus, (4). thalamus, and (5). cerebellum. ANOVA demonstrated significant main effects for BOLD signal amplitude ( p<0.05) changes in all AOI. Similarly, ANOVA showed significant differences in the volume of activation ( p<0.05) with increasing stimulus intensity in four AOI. Secondary analyses of pooled data showed increasing probabilities of activation at higher stimulus intensities within each AOI. Collectively, these data indicate a dose-response relationship exists between lower extremity NMES and brain activation in specific neural regions. The current results, while limited in their generalizability, are foundational for future studies of interventions using NMES.

My comments:
I think this is a very interesting study that I read about a year ago.  I find myself talking about it frequently with my patients when I find EMS (semantically the same as NMES) working better than I expect. EMS is used primarily for muscle strengthening but has been found to be more effective than TENS for pain reduction, works exceptionally well for neuropathy/neuropathic pain, and I have seen it immediately eliminate arm tremors in a patient. The patient had gone through a bastion of tests at Barrow Neurological, been diagnosed with conversion disorder, then after a 12 minute EMS treatment the tremors were gone.  I thought of this again yesterday when I was treating a 74 year old patient for poor balance, neuropathy, back and neck pain all with a combination of exercise and EMS. She reported all of her other pain had resolved but she had elbow pain which I diagnosed as lateral epicondylitis/tennis elbow. I didn’t want to spend much time treating the elbow as I thought  it was the least of her worries. I wanted to continue to work on fall prevention with general strengthening, balance and agility training. She also had a history of dropping light objects, she calls it her “dropsies”, but over the course of her treatment said it been reduced ~50%. Her muscle strength was much improved so weakness was not a reason for her dropping objects. Long story shorter, I decided to add reverse wrist curls to her exercise program and did EMS to her biceps, triceps, and forearm muscles with a hope to further increase UE strength and lessen pain.  After one treatment and following a weekend she reported her dropsies had decreased another 30-40%, which is pretty big improvement over one intervention. So the next day I applied EMS to her arm again but also added in my hand grip electrode to provide EMS through the palm of the hand.  So, on her next visit I will see what she has to say. Even though I treated the arm reluctantly, I maybe came up with a new understanding and breakthrough with her, which I can hopefully apply to other patients.

When you are using multiple interventions (which is generally the case in physical therapy) to treat a problem it is sometimes impossible to say what does what and how much. Also there is a lot of overlap between each intervention (strength exercise, balance exercise, coordination exercise, EMS) and what you are hoping to achieve. However, this patients rapid response was much faster than one would expect from a single day of exercise and I think most likely due to the EMS working on the muscles in the arm and hand and also increasing activation and blood flow in the brain as found in the above quoted study. It’s also interesting that brain activity was seen in a dose response manner, in that more intense EMS causes more of a brain response. This perhaps strengthens neural connections and improves nerve conduction velocity resulting in improved coordination. I am starting to see this in other studies as well. What’s also interesting is all the areas of the brain that are affected. Electric muscle stimulation applied to the study participants’ quadriceps increased blood flow to the primary sensory cortex, primary motor cortex, cingulate gyrus, thalamus, and cerebellum with blood flow always increasing more so in the brain as intensity levels of electrical stimulation was applied to the study subjects leg muscles.